Universal joints, also known as U-joints or Cardan joints, are used to couple two shafts and facilitate the transfer of force from one shaft to the next. Typically, each shaft will have a double yoke ending on the ends to be joined. A cross-shaped universal joint with four arms, or pins, connects the two shafts by placing one pin in each of the four yokes. This type of connection allows each shaft to rotate on an independent, and sometimes dynamic, axis.
Universal joints are found in industrial, military, and consumer applications. Typical products using universal joints include boats, cars, planes, generators, and other situations in which two shafts must be connected by a flexible joint. Common applications in vehicles include the drive-train and steering system. Often the forces transmitted with a universal joint are extremely large. Some of the most common applications in which universal joints are used in extreme conditions is four-wheel drive, off-road automobile driving and automobile and boat racing.
Four-wheel, off-road driving has become an increasingly popular pastime in recent years. Numerous clubs, magazines, and auto-part makers dedicate significant attention to the growing niche of extreme off-road driving. Many enthusiasts consider off-road driving the ultimate test of automotive engineering. Vehicles and components are literally driven to their breaking points in difficult driving conditions.
Off-road driving applications include driving through small rivers, over large rocks, through sand, through mud, through snow, over fallen trees, and even over other cars, Four-wheel-drive vehicles are most common for these types of applications. Even most four-wheel-drive vehicles require significant modifications from the factory-produced models to handle treacherous off-road driving conditions.
Numerous companies produce after-market products designed to allow cars and trucks to handle off-road driving conditions. Typical products added to a vehicle to allow off-road driving include rugged tires, stronger axles, heavy-duty shock absorbers, gear differentials, and transfer cases. Even with the best modifications and the most skillful drivers, component failures are commonplace.
Universal joints are among the more common trouble-areas for off-road vehicles. In automotive applications, universal joints are used in a number of places and are particularly important for connecting a vehicle's drive shaft and axles. In such applications, the universal joints can be subjected to extreme forces as the connected shafts spin with high torque and high rpm.
When the universal joint leading to one particular axle fails, the force from the drive shaft can no longer be distributed that axle. Such a failure will render the associated tire immobile. When a vehicle suffers a universal joint failure, the vehicle will frequently need to be will towed to a repair facility. Furthermore, the types of repairs required after a vehicle suffers a universal joint failure generally need to be performed in a repair facility with sophisticated lifts and other equipment making such repairs very expensive. Moreover, failure of a universal joint often results in other problems such as broken axles or broken drive shafts.